Heretofore in wide use as motor vehicle evaporators are those of the so-called stacked plate type which comprise a plurality of flat hollow bodies arranged in parallel and each composed of a pair of dishlike plates facing toward each other and brazed to each other along peripheral edges thereof, and a louvered corrugated fin disposed between and brazed to each adjacent pair of flat hollow bodies. In recent years, however, it has been demanded to provide evaporators further reduced in size and weight and exhibiting higher performance.
To meet such a demand, evaporators have been proposed which comprise a pair of upper and lower tanks arranged as spaced apart vertically, and a plurality of tube groups arranged in two rows as spaced apart forwardly or rearwardly of the evaporator between the pair of tanks and each comprising a plurality of heat exchange tubes arranged in parallel at a spacing laterally of the evaporator, the heat exchange tubes of each tube group having upper and lower ends connected respectively to the upper and lower tanks, a louvered corrugated fin being disposed in an air passing clearance between each adjacent pair of heat exchange tubes of each tube group, the lower tank having a horizontal flat top wall (see, for example, the publication of JP-A No. 2001-324290), or the lower tank having a top wall wherein an intermediate portion with respect to the forward or rearward direction is highest and which is so shaped that the highest portion is gradually lowered toward both the front and rear sides (see, for example, the publication of JP-A No. 2003-75024).
The evaporators disclosed in these two publications are made smaller in size and weight and exhibit higher performance than evaporators of the stacked plate type, and are therefore increased in the amount of water condensate produced relative to the heat transfer area.
Consequently, a relatively larger quantity of water condensate becomes collected between the top wall of the lower tank and the lower ends of the corrugated fins, and is likely freeze to result in impaired evaporator performance.
An object of the present invention is to overcome the above problem and to provide an evaporator which is reduced in the amount of water condensate that will collect on the top wall of the lower tank.